1. Field of the Invention
The present invention relates generally to medical devices and a method of using them for selectively affecting the temperature of a patient's body, or a portion of the patient's body, and more particularly, to a temperature control catheter system including an on-board temperature probe and a method of use thereof.
2. Description of the Prior Art
Under ordinary circumstances, the thermoregulatory system of the human body maintains a near constant temperature of about 37° C. (98.6° F.), a temperature generally referred to as normothermia. For various reasons, however, a person may develop a body temperature that is below normothermia, a condition known as hypothermia, or a temperature that is above normothermia, a condition known as hyperthermia. Accidental hypothermia and hyperthermia are generally harmful, and if severe, the patient is generally treated to reverse the condition and return the patient to normothermia. Accidental hypothermia significant enough to require treatment may occur in patients exposed to overwhelming cold stress in the environment or whose thermoregulatory ability has been lessened due to injury, illness or anesthesia. For example, this type of hypothermia sometimes occurs in patients suffering from trauma or as a complication in patients undergoing surgery.
However, in certain other situations hyperthermia and particularly hypothermia may be desirable and may even be intentionally induced. For example, hypothermia is generally recognized as being neuroprotective, and may, therefore, be induced in conjunction with cardiac surgery where there is an interruption or decrease of cardiac output of oxygenated blood, treatments for ischemic or hemorrhagic stroke, blood deprivation caused by cardiac arrest, intracerebral or intracranial hemorrhage, head and spinal trauma, brain or spinal surgery, or any other situation where there is danger to neural tissue because of ischemia, increased intracranial pressure, edema or other similar processes.
Other examples where hypothermia may be neuroprotective include periods of cardiac arrest in myocardial infarction and heart surgery, neurosurgical procedures such as aneurysm repair surgeries, endovascular aneurysm repair procedures, spinal surgeries, procedures where the patient is at risk for brain, cardiac or spinal ischemia such as beating heart by-pass surgery or any surgery where the blood supply to the heart, brain or spinal cord may be temporarily interrupted.
Hypothermia has also been found to be protective of cardiac muscle tissue when that muscle tissue is at risk, for example during or after a myocardial infarct (MI), or during cardiac surgery, cardiac arrest, or other situations where there is deprivation of the normal blood supply to the cardiac tissue. Indeed the tissue protective nature of hypothermia in general is recognized in a vast array of situations.
Simple surface methods for cooling such as cooling blankets, immersion in cold water or ice baths, or alcohol rubs are generally ineffective for inducing hypothermia. The body's normal thermoregulatory responses such as vasoconstriction of capillary beds at the surface of the body and arterio-venous shunting of blood away from the skin act to render such cooling methods ineffective. Further, if the body temperature drops sufficiently below normothermia, usually at about 35.5° C., the body begins to shiver as a thermoregulatory response to generate additional metabolic heat and fight the induction of hypothermia. This may increase the generation of metabolic heat by 200-500% and generally makes induction of hypothermia in an awake patient impossible by surface cooling alone. Further, the shivering itself is so uncomfortable and exhausting for the patient that this is altogether unacceptable for an awake patient. Only if the patient is paralyzed, which necessitates the patient be intubated for breathing and be placed under general anesthesia can the patient be subjected to significant surface cooling. Even under these conditions, surface cooling which necessitates cooling through the skin and surface fat layers and the use of generally low power surface cooling devices, is too slow and inefficient to be an acceptable means of inducing therapeutic hypothermia.
Furthermore, if control of the patient's temperature is desired so as to attain and maintain a target temperature (sometimes but not always normothermia), or to reverse hypothermia and re-warm the patient at a predetermined rate, surface cooling and warming far too slow and inefficient to give the required level of prompt and precise change in the patient's core temperature to allow these methods to control the patient's thermal condition.
A patient's temperature may be controlled by a very invasive method of adding heat to or removing heat from a patient's blood, particularly in the case of heart surgery. Blood is removed from a patient, circulated through a heart-lung by-pass system, and reintroduced into the patient's body. The equipment generally has a temperature control unit that heats or cools the blood as it is circulated out of the patient before it is reintroduced into the patient. Because a large volume of blood is circulated through the machine in a short time, this by-pass method may be both fast and effective in changing the patient's core temperature and in controlling that temperature, but has the disadvantages of requiring a very invasive medical procedure which requires the use of complex equipment, a team of highly skilled operators, is generally only available in a surgical setting where the patient has undergone a thoracotomy (had its chest split and opened), and involves mechanical pumping of a huge quantity of the patient's blood and channeling that blood through various external lines and conduits, all of which is generally very destructive of the blood tissue resulting in the cytotoxic and thrombolytic problems. In fact, most surgeons using such by pass machinery tend to avoid its use for longer than four hours, much less if at all possible, which is an inadequate period of time for treatment of some conditions such as stroke.
One method for adding or removing heat from a patient by adding or removing heat from the patient's blood that does not involve pumping the blood with an external, mechanical pump is by placing a heat exchange catheter in the bloodstream of a patient and exchanging heat through the catheter. This endovascular temperature management (ETM) technique was described in U.S. Pat. No. 5,486,208 to Ginsburg, the complete disclosure of which is incorporated herein by reference. The Ginsburg patent discloses a method of controlling the temperature of a body by adding or removing heat to the blood by inserting a heat exchange catheter having a heat exchange region into the vascular system and exchanging heat between the heat exchange region and the blood to affect the temperature of a patient. One method disclosed for doing so includes inserting a catheter having a heat exchange region comprising a balloon into the vasculature of a patient and circulating warm or cold heat exchange fluid through the balloon while the balloon is in contact with the blood.
In successful ETM, in addition to fast and precise changes in a patient's body temperature, fast and precise control over a patient's thermal condition is very important whether the patient is being cooled, warmed, or maintained at a constant temperature. A general apparatus and method of ETM control based on temperature management responsive to feedback from temperature probes in or on the patient is disclosed in U.S. Pat. No. 6,149,673 to Ginsburg, the complete disclosure of which is incorporated herein by reference. A similar method is described in PCT publication WO 01/10494 to Radiant Medical Inc., the complete disclosure of which is also incorporated herein by reference. In such methods, a signal representing the temperature of a target tissue, which as mentioned may be the core body temperature, is directed to a controller from a temperature probe inserted on or in the patient, and the controller then controls the exchange of heat between the heat exchange catheter and the patient's blood flowing past that catheter. That in turn controls the temperature of the patient. With such a method, it is clear that precise, accurate and convenient control is dependent to a large extent on the precise, accurate, and convenient temperature measurement of the temperature of the target tissue (which may be the core body temperature) and thus dependent on a precise, accurate and convenient temperature probe.
Currently, the patient's temperature may be measured by any one or several generally available temperature probes. These include, for example, skin temperature probes, tympanic probes that may be placed in the ear canal and perhaps even in physical contact with the ear drum, esophageal probes including nasoesophageal probes, rectal probes, bladder probes, temperature sensors placed on an insertion sheath, and temperature probes that may be inserted by needle directly into the target tissue. Each of these techniques, however, suffers from significant shortcomings.
Some probes may not give an accurate temperature of the target tissue and therefore may not provide the information necessary for controlling the ETM procedure. For example, if the target is the core temperature of the patient, a skin temperature is generally not an accurate representation of the core temperature; if cardiac muscle is the target tissue, a bladder probe might not be sufficiently accurate. The probe might not be sufficiently responsive to changes in temperature to provide a current temperature of the target temperature. For example, a rectal temperature probe is generally very slow to respond to temperature changes in the core, and thus if the controller is receiving its temperature signal from a rectal probe, it might not be able to respond with sufficient speed and precision to changes in the core temperature. Bladder temperature probes also tend to suffer from this problem. Some probes are awkward and too difficult to use. For example, tympanic probe are difficult to place and tend to fall out and thus not provide an accurate temperature measure. Where a temperature probe is controlling an ETM procedure and thus in the patient at the same time as an ETM catheter, it may reflect the temperature of the ETM catheter rather than the target tissue if the probe is located too close to the catheter. Probes placed on the insertion sheath, for example, may tend to be unduly influenced by the heat exchange catheter placed through the sheath. Other probes may measure the temperature of the target tissue, but have other disadvantages that make their use undesirable. For example, needle temperature probes that are stuck directly into the target tissue, of course, measure the temperature of the target tissue, but are invasive and require the patient suffer an additional needle stick. They are also dependent on accurate placement in the first instance which may be a difficult and highly skilled procedure, and require that they do not move after placement, requiring constant monitoring and taping or the like which may be obtrusive and awkward.
If redundancy is important for safety, as it usually is in a controlled ETM procedure, all of the above devices would generally require the placement of two probes. This may require two probes placed in different locations that may reflect different temperature profiles, a very real problem for controlling ETM. It may require that two probes be attached together, which makes the probes large and often clumsy to use.
Very importantly, when used to control an ETM procedure, all of the above require a device (the probe) in addition to the ETM catheter already being inserted into the patient's body. These are generally separately placed requiring an additional procedural step, are often quite distal to the insertion site of the catheter but must still be attached to the controller that is attached to the ETM catheter. This may greatly complicate what may already be a crowded operating room or other area and add undesirable complexity to the procedure.
For ETM to accurately control the temperature of a target tissue, it is important that the temperature measured by the probe provides current and accurate measurement of the temperature of the target tissue and responds quickly to changes in temperature of the target temperature. This is not always the case with the probes mentioned above. If the controller precisely and rapidly responds to the temperature feedback to control the temperature of the target tissue, for example if the patient's temperature is being increased at a very precise rate of, for example, 0.2 C per hour, the controller must act to add heat when the temperature is not increasing fast enough, remove heat if the body is adding metabolic heat so fast that it would result in rewarming too fast, or maintain the temperature of the heat exchange catheter the same as the blood if the patient's temperature is increasing at exactly the correct rate. The systems described in the publications incorporated above may be capable of such precision, but rely on temperature information from the temperature probes that is current and accurate.
Temperature probes placed directly in the bloodstream in one of the great vessels such as the inferior vena cava (IVC) generally accurately reflect the core body temperature which is also generally the temperature of the brain or heart tissue, currently the two most common target tissues for ETM, but if the probe is placed some distance from the heat exchange catheter such placement usually involves an additional incision or puncture into the vasculature, and if the probe is placed in the same general vicinity as the heat exchange catheter, there is a likelihood that the temperature reading will be unacceptably influenced by the heat exchange region on the catheter or the temperature of the catheter shaft and thus not represent the temperature of the target tissue sufficiently to serve as a control temperature for the system.
Further, when the temperature probe is placed in the vasculature in general, the distal tip of the probe which generally houses the temperature sensor itself may come into contact with the wall of the vessel. In such a case, the temperature that is sensed will be that of the vessel wall and not of the blood. While these two temperatures may often be the same, there will be occasions where they may be unacceptably different. Furthermore, the distal tip of such a probe must be designed so that it will not be traumatic to the vessel wall. It would be best, of course, if contact with the vessel wall could be avoided altogether.
When any device is inserted into a patient, the physician generally would prefer to make as small an incision or puncture as possible. Thus where a probe is inserted into the bloodstream, a low profile is generally preferable. If the probe is attached or otherwise associated with another device that is being inserted into a patient, a means to keep the overall profile to the device being inserted would be desirable.
Accordingly, it would be helpful to have a temperature probe that was easy to place in conjunction with an ETM procedure.
It would also be helpful to have a temperature probe that precisely and accurately measured a relevant tissue temperature for ETM.
It would also be helpful to have a temperature probe that rapidly responded to changes in temperature in a target tissue.
It would also be helpful to have a temperature probe that did not create additional crowd the treatment area during treatment by ETM.
It would also be helpful to have a temperature probe that did not require additional punctures or incisions in a patient undergoing ETM.
It would also be helpful to have a temperature probe that had a deployed and an undeployed configuration.
Accordingly, it would be helpful to have a temperature probe located in the blood stream at a location close to the heat exchange catheter to accurately measure the temperature of the blood but not be unduly influenced by the temperature of the heat exchange catheter.
It would be helpful to have a temperature probe that had a plurality of temperature sensors for redundancy and safety.
It would be helpful to have a temperature probe that had an atraumatic distal tip.
It would be helpful to have a temperature probe that could be advantageously inserted into the vasculature of a patient undergoing EMT without the need of a second incision or puncture.
It would be helpful to have a temperature probe that was an on-board temperature probe.
It would be helpful to have a temperature probe that had a deployed and an undeployed position, wherein the operator could move the probe between the deployed and the undeployed configuration.
Furthermore, it would be helpful to have a system and method that ensure that the temperature reading provided at the heat exchange catheter is accurate in order to ensure appropriate operation of the heat exchange catheter.